The membrane biofilm reactor (MBfR) has been described for use in the decontamination of wastewater streams. In a typical MBfR device, as described, for example, by Rittman in U.S. Pat. No. 6,387,262, a matrix of hollow-fiber membranes provides a growth surface for a biofilm of microorganisms capable of metabolizing contaminants in an influent stream. For example, for reductive elimination of high oxidation state contaminants, such as nitrate or perchlorate, hydrogen gas, typically under pressure, is introduced into the lumen of hollow-fiber membranes, where it diffuses through the walls of the membrane to contact a biomass growing on the external surface (outside) of the membranes. Alternatively, an oxygen-containing gas, such as air, enriched air, or oxygen, may be introduced into the hollow fiber membranes to fee the biomass made of organisms able to remove oxidizable contaminants, such as ammonia or various organic compounds.
High packing density of the hollow-fiber membranes improves the efficiency of MBfR, in principle, by increasing the operable surface area of biofilm growth. However, high packing density can also lead to biofouling, which increases operating costs by reducing influent flow and requiring periodic maintenance to the MBfR (e.g. backwashing, disassembly, cleaning, etc.). Biofouling is evidenced by an increased pressure drop across the MBfR device, which is generally accompanied by an increase in the residual contaminant levels.
Thus, the need exists for MBfR devices and systems that maximize packing density while minimizing biofouling.